how to send SOAP request with SSL certificate in P

I'm trying to send a SOAP - PHP request with a DER certificate (that means the certificate don't have a privateKey) but no success.

$local_cert = FULL_PATH_TO_MY_CERT;

   $client = new SoapClient($wsdl, array(
                'local_cert' => $local_cert,
                'trace' => 1,
                'exceptions' => 1,
                'soap_version' => SOAP_1_1,
                'encoding' => 'ISO-8859-1',
                'compression' => (SOAP_COMPRESSION_ACCEPT | SOAP_COMPRESSION_GZIP),
                'location' => 'https://webserviceurl:port/ws/servlet/ws'
            ));

Only I recieve this errors:

Warning (2): SoapClient::SoapClient() [soapclient.soapclient]: Unable to set private key file `PATHTOMYLOCALCERT' [APP\Vendor\WebServices\MyWS.php, line 206]

Warning (2): SoapClient::SoapClient() [soapclient.soapclient]: failed to create an SSL handle [APP\Vendor\WebServices\MyWS.php, line 206]

Warning (2): SoapClient::SoapClient() [soapclient.soapclient]: Failed to enable crypto [APP\Vendor\WebServices\MyWS.php, line 206]

Warning (2): SoapClient::SoapClient(https://webserviceurl:port/ws/servlet/ws?wsdl) [soapclient.soapclient]: failed to open stream: operation failed [APP\Vendor\WebServices\MyWS.php, line 206]

Warning (2): SoapClient::SoapClient() [soapclient.soapclient]: I/O warning : failed to load external entity "https://webserviceurl:port/ws/servlet/ws?wsdl" [APP\Vendor\WebServices\MyWS.php, line 206]

but I've found a little trick (in php.net) using the function file_get_contents($local_cert); the errors are gone.

But a new error come from.

Result : string(773) "Error reading prefix:Action.Execute"

What I mean is... this error above... is comming from the WebService? because it cannot authenticate with my request?

Thanks everybody. (appreciate your answers)

I'm using SSL certificate in my soap call.

In My case I'm giving absolute path on my server for wsdl and for local_cert I've already defined those in my class. Please note that I'm using my certificate in .pem format.

public $local_cert = "/var/www/.../webroot/cert.pem";
public $wsdl = "/var/www/.../webroot/my_wsdl.wsdl";

$this->client = new SoapClient($this->wsdl, array(
        "trace"         => 1, 
        "exceptions"    => true, 
        "local_cert"    => $this->local_cert, 
        "uri"           => "urn:xmethods-delayed-quotes",
        "style"         => SOAP_RPC,
        "use"           => SOAP_ENCODED,
        "soap_version"  => SOAP_1_2 ,
        "location"      => $this->location
    )
);

In my certificate there are 2 parts. Certificate and RSA Private Key.

(1)-----BEGIN CERTIFICATE-----
MIIFjzCC....
....
-----END CERTIFICATE-----
(2)-----BEGIN RSA PRIVATE KEY-----
MIIEpAI....
....
ww==
-----END RSA PRIVATE KEY----

And most important you should use https link for making a soap call. This is working fine for me.

Hope this will help you.